Precoating in filtration



Feb. 6, 1934. E. sTARlTzKY PRECOATING IN FILTRATION Feb. 6, 1934. EsTARn-ZKY 1,946,039

' PRECOATING IN FILTRATION Filed llay 21. 1951 5 Sheets-Sheet 2' Feb. 6,1934. E, STARITZKY v1,946,039

PRECOATING IN FILTRATION ,Patented Feb. e, 1,934

UNiTEDsTATEs PATENT. oFFici.

PRECOATING 1N FILTRATION Ware Application May 21, 1931. Serial No.539,117

6 Claims.

This invention relates to improvements in continuous filter operation.More particularly it relates to improvements in the way of iilter aids.That is, to means which make possible the satisfactory filtration ofdifficult filtrants, such as pulps which are liable to blind the filtermedium by reason of their colloidal nature, causing reduced filtercapacity, sluggish cake discharge, and other troubles. The object is tomake the iilter capable of continuous operation with such materials.

The invention has its preferred use in those industries where the filteraid material to be eniployed for fine pulp filtration is available fi'omthe manufacturing process itself, and where it also forms a desirableingredient in the final cake, as for instance in certain steps of starchmanufacture. For these and other reasons the invention also relates tothe adaptation of my improvements to a specific process of cornstarchmanufacture described hereinafter.

Advantageously, although not exclusively, this invention is applied tothe so-called internal type drum iilter, that is, the type where thedrinn itself forms the. trough for the bath of pulp 'from which theliquid is filtered. It is an essential characteristic of the internaltype drum filter to allow the coarse particles in a fine pulp to settleout first downwardly upon the filter-medium, allowing the coarse solidsto form a bed for the majority of the fines to settle upon, andpreventing too intimate a constant between the fines and the filtermedium. I This is incidentally the feature which has favored thedevelopment of external type Where the drum operates in an exteriorseparate pulp trough in which undesirable settling of the coarseparticles takes place.

I describe the features of my invention essentially in connection withthe preferred internal drum type, which furnishes the mostcharacteristic embodiment I am aware of at present. I wish however toinclude into the scope of my invention other continuous lter types aswell. for instance the external drum type, the plane rotary type, orothers, and I contemplate having my invention embodied therein.

` The main feature relates to having the filter medium rst separatelycoated with some substance which is more easily filterable than thematerial to be filtered, as I have found that by such pre-coatingunusual, new and superior results can be obtained, especially withcertain filtrants which to my knowledge have hitherto refused to submitto any known method of conthe internal type drum lter over the so-called(ci. 21o-2oz) tinuous filtration on a satisfactory commercial scale.

I am aware of the fact that the method of applying filter aids in theform of a pre-coat has been practiced in discontinuousor intermittentfashion with filter presses. The procedure in such batch operation hasbeen, tofilter coarse pulp and ne pulp successively whereby a compositecake was formed consisting of a base of coarse, and a top layer of nematerial. discharging the cake from the compartments of vthis stationarymachine, it was ready for a new batch. My invention advances over thispractice by improvements of structure and operating method in thecontinuous type of filter.

When handling some such materials in continuous filters the fines willblind and foul the filter medium blanketing the same in a thinimpervious layer. With other materials, the filter cake will crack inthe drying zone 'and the individual pieces 75 or islands will clingobstinately to theiilter cloth, resisting discharge, whereupon thefilter blowback discharges quite ineffectively through the cracks. Inboth cases the efficiency of the filter operation is seriously impaired,capacities low-.80 ered andthe discharged cake is too high in moisturedue to poor suction through a partly blinded or improperly cleaned.vfilter medium. .In other words the process is too ineilicient to besatisfactory in continuous operation. 35

The present invention advances specifically over an older method ofoperating internal'drum filters, in which a certain amount of coarsematter in afine pulp isv allowed to settleout or segregate first uponthe filter medium allowing the majority of the slower settling fines todeposit thereon, the tendency being to prevent too intimate a contact ofthe nes with the lter cloth. Another suggestion along that line has beento admix coarse material or filter yaid, if such was lacking in thepulp, in an amount which will help to sustain the above conditions.According to this invention, a pre-coat of filter aid material iscontinuously applied to the internal drum filter medium, allowing a typeof filter aid and filtrant to be handled in the filter, which will notreadily segregate when in mixture.

My method of continuous pre-coating is superior to the known expedients,in that it produces a distinct, controlled stratification of thecake,and I have found that certain materials will not ltersatisfactorilyin continuous filters until handled in this manner.

In the preferred internal type of drum filter, this' invention lendsitself to a simple and prac- 110 After 65 A fines thereon, to the endofobtaining a 'cake of.

tical embodiment. A suitable baille attachment or partition arrangedwithin the druml may divide the lower portion thereof into twolongitudinal compartments, which are to receive separately the coarsematter or filter aid, and the fine pulp respectively. Marginal iiexiblestrips may seal the compartments against excessive leakage from one toanother, vthe clearance between the lower edge of the baiiie and thedrum being adjustable and arranged to admit the desired thickness ofcoarse material into the fine pulp compartment. Upon the coarse solidsdescend the ner or colloidal sizer solids covering the bed, until it hasreached the proper thickness, making a cake of desired properties andcomposition.

' In this way the fines are prevented from reaching thefllter medium orcloth. Fine particles which tend toinvade the coarse layer are arrested`in the tortuous passages thereof. e Thus the suclayer is unimpeded,offering the full benefit of the draining action of the coarse layer forthe maximum dryness at a minimum of operating cost.4

Consequently a relatively thicker layer of fines maybe formed,while.thepsuctionoperates to re- 'trace left upon the cloth to impair orupset efflcient continuous operation.

In the example of cornstarch manufacture de- -scribed hereinafter, thecoarse matter or filterA aid is available in the form of a pulp incertain quantities incidental to the Vmanufacturing process in which thefine pulp is to be filtered. The coarse matter in lquestion is of thetype which does not segregate readily when mixed with thev finefiltrant. With the present arrangement in an.

internal drum filter, the two pulps can be filtered in two adjacentcompartments of one and the same filter in an efficient and economicalmanner. As they yield simultaneously from the process, a cake resultswhich presents a desired combination of coarse plus fines whichisgenerally used for stock feed purposes. t

A feature of refinement in the preferred interfiltering characteristicsof the pulps, and whichl may be provided for by suitable arrangement inthe well known master valve ofthe filter.

In this way the relative effective filter areas of the compartments maybe adjusted with re-` gard to the ltering characteristics, there beingalso the requirements that a certain minimum of the cycle must beallotted to the pre-coating action, requiring at least onefully-submerged vfilter panel.

It is important to note that with these refine- A ments it is possibleto maintain at all times in the pre-coating compartment an equal orhigher hydrostatic level than in the fine pulp compartment. This isIimportant lest the level in the pre-coating compartment should everunduly drop, and induce an' undesired fiow from the fine pulpcompartment, by which some of the fine filtrant would come in .directcontact with the cloth.

Another feature `of my invention is the arrangement lby which theadjustable baille is timed, and set with relation to the zones ofdifferential suction.

My improved method and apparatus are preferably employed in the glutenfiltration step in a process of cornstarch manufacture. In such astandard process the corn is mechanically comminuted in a certainmanner, in order to liberate the starch, and the product is thensubmitted to a number of wet classification or starch washing steps, inwhich are usually eliminated three grades of impurities or by-products.

The commercial grade of pure starch is obtained'from these eliminationsteps, and the byproducts consist of the cellular or tissuey substancerecovered chieiiy as bran, and grits, and the proteins which form theessential constituent of the so-called` gluten.

These products though recovered separately and by different methods, areusually combined before marketing and together form a by-product of thecornstarch manufacture, which is used as stockfeed. A

According to my tests I attain the most satisfactory results in thefiltration of gluten when using the fibrous by-products preferably thegrits, or a mixtureof .grits and bran as a pre-coating material.

In thev conventional process the thin gluten sludge as recovered fromthe starch Washing tables, is dewatered by sedimentation 'followed byfiltration usually in filter presses whereupon the moisture is furtherreduced to the desired degree in rotary driers. With my improvements,the

economical use of continuous vacuum filters is` I now possible in thisstep with a material previously-not well suited for filtration by thecontinuous process.

My .improvements also alleviate or overcome certain irregularities ofoperation encountered in the general plant performance. It is commonknowledge that corn which has been superheated in storage or duringtransportation yields gluten which is extremely difficult to filter.HWhen handlingsuch corn, the filtration foperation presents considerablediiculties to the manufacturer and this operation usually forms. thebottle neck which reduces the capacity of the plant in accordance withthe variations of the nature of the corn. By applying my invention, itis possible to maintain more uniform capacities of` the lter i andhence, of the entire plant.

In standard practice, the gluten is recovered yin the last starchwashing as tailings from the starch washing tables. It is f fine orcolloidal size and contains essentially proteins and residual o starch.`As the starch content varies with the "efficiency obtained in theoperation of the starch trol of v:filter speed, amount of suction etc..in

order to obtain maximum eiiiciency. Gluten for instance, normallyrequires such close control and then usually forms a thin imperviouslayer upon the lter cloth which will discharge onlyincompletely unlessscrapers or other forceful means of cake discharge are used, which areinjurious lter products are obtained at all times and at l a more evenrate.

While a particular example of the method of, and apparatus arrangementfor, carrying out the invention, have been described in detail for thepurpose of disclosure, it is to be understoodthat the invention is notlimited to such particular example as to method and apparatus, butcontemplates all such variations and modifications thereof as fallfairly within the scope of the appended claims, for instance whereas aninternal type drum lter has been shown and described herein, theinvention may be applied to an external type of drum lter.

Drawings of a preferred embodiment of my invention are attached heretoin which:

Fig. 1 shows a Vertical sectional view through a pre-coating lter.

Fig. 2 is an enlarged cross-sectional View through .the pre-coatingfilter, taken along the line 2-2 in Fig. 1.

Fig. 3 is a View upon the valve end of the lter.

Fig. 4 is a detail view upon the master valve with the valve coverremoved. I

Fig. 5 is a View upon the inner side of the master valve cover.

For the purpose of illustration, this invention is shown to be embodiedin a rotary drum filter of the internal suction type, with an endwisecake discharge. It consists of a cylindrical shell 10, which is hereinshown to be formed of wooden slats for acid resistance. The rear end ofthe drum is formed by a wall or end plate l1, which has an opening 12over which is mounted a hollow trunnion member 13 which carries at itsrear end the usual master valve mechanism 14 hereinafter described. Thedrum has provided thereon the ordinary longitudinal lter sections orpanels 15, with a iilter backing shown at 16 and the filter mediumproper at 17. The front end of the shell is formed by an annular endplate 18 with an opening 19 through which the the rear by a journal 23in which it carries said trunnion member 13, said journal anchored upona base 24. The front end of the drum operates in the usual manner uponsupporting rollers 25 through a circular track rail 26 fixed upon shell'10. The drum is driven through a worm gear 27 fixedupon jthe trunnion 13and meshing with a. worm 28 having bearings anchored upon the basev24,-'the worm shaft carrying at one end the drive pulley `29.

The trunnion member I3 forms part of the' usual master valve by whichsuction and pressure respectively are distributed to the individual lterpanels of the drum. Within the trunnion are mounted the ends ofvpressure or suction distributing pipes 30,`terminating in slot-likenarrow openings 31 (see Fig. 4),- and leading in an S-shaped curve eachto one individual lter panel of the drum. The master valve cover 32 tsover the open end of the trunnion'membertocovez` said distributingopenings 31. The cover Vis held stationary in properly adjustedpositionfby the torque rod 33 while the drum rotates, the valve cover being heldupon its seat by spring members 33a and 33h mounted upon beam membershereinafter to be described. Suction and pressure are,

is provided with means for producing diierential suction zones in thelter, such as willbe present- 1y described, and it also providesv forthe usual cake blow-oli zone.

The master valve cover 32 is'in the form of a U-shaped channel formingan .annular groove 32a, which covers the distributor openings 31, and inthe groove are placed adjustable partitions 34 and 35, or so-calledbridges which determine the various suction and pressure zones -of thefilter (Fig. 5). These bridges 34 and 35 are adjustable within thegroove or channel of the cover, and settleable as by set screws 36 and37. A member 38 denes by the length of its hollow 39 the range of thecake blow-off zone, and it must be adjusted to correspond to thelocation of the cake receiving device within the filter drum. Pressureenters through an opening or nozzle 40 in the blow portion of the mastervalve.. A suction nozzle 41 draws from the pre-coating zone the range ofwhich is defined by the length of space between the bridges 34 and 35.Another nozzle 42 draws from the main filtering portion of the mastervalve which accordingly lies past the bridge 35. The numeral 42aindicates a connection in the cover with the atmosphere for the purposeof releasing theO pressure in the panels.

after the same have passed the blow-oir zone,

which connection may also be used for introducing a pressure uid intothe panels for cleaning the filter medium.

The filter drum in the present embodiment is shown to be of considerablelength, and has a conveying mechanism extending within the drum for cakedischarge. The ltercake is dropped from the top portion of the drum intoa longitudinal hopper 45 arranged in suitable position below the top-portion of the drum and it is carried outof the interior by means of anendless belt conveyor 44. The supporting structure for the cakedischarge mechanism or conveyor includes a main beam 46 consisting ofthe companionfmembers or channels 46a and 46h extending longitudinallythrough the entire drum, project# ing through the front opening thereofand also through the central hollow in the trunnion member 13 and themaster valve 14. The front end of the beam is supported by a rigidstructure in the form of a stand 47, the rear support of the beam beingmerely indicatedin the drawings by member 48. An auxiliary beam orchannel iron 49 is braced through suitable rigid connections from thesaid main beam, both beams forming the mountings for the\end rollers 50and 51 of vthe beltuvconveyor, and in addition thereto for theauxiliaryidlers 52 supporting the upper or active run of the conveyorbelt. The conveyor mechanism of coursel may include suitable takeup andadjusting means 53 and 54'as shown at each end of the conveyor foradjusting the end rollers thereof. y

lThe iilter drum so far described is of substanvtialy standard design.-An attachment or adjustable baille wall 55, as most clearly shown inFig. 2 constitutes the mechanical improvement inv this filter accordingto one specic embodiment of this invention, and which makes it possibleto provide two successivev longitudinal pulp com partments connectedwith the lter drum. The one compartment filled with pre-coating materialcauses a lter panel passing therethrough Vto be covered withapreliminary coat of coarse or pre-coating material, the succeedingcompartment being the main filtering compartment in which the fines of apulpare filtered upon said preliminary layer.Y The baille 55 thus mayform a common dividing wall between the two pulp compartments wherebytwo adjacent pools of different materials are maintained in contact withthe lter drum. f

The novel attachment 55 consists of a baille or partition 56 which isherein shown to be of wood, and mounted with marginal strips 57 ofilexible or other suitable material for sufficient contact y and propercooperation between the baille and the adjacent portions of the drum. Astrip 58 along the lower edge provides a suitable ,working z lyadjustable within certain limits, that is` radialit is fixed upondepending members 69, 70

ly and angularly adjustable to meet -various operating conditions in thefilter. the suspension rods 60 are shown to be threaded and extendingplungerlike into the interior of the baille wall. A hollow 63 in the'baille accommodates the lower end of the suspension rod and also a nut64-thereon which is accessible through opening 65, a lock nut 66 beingshown at the upper end of the suspension rod in order to fix the settingof the rod in therbaille.

After the radial length of the baille is determined the baille may begiven the proper operating relationship, that is clearance with thesurface of the .iilter mediumby means of a settable member 67 againstwhich the weight ofthe sus, pended baille wall is allowed to rest, thusdetermining the angular position of the baille. The member 67 is clearlyshown in Fig. 2 as having screw and slot connections 68 and 68a. bywhich of the conveyor structure. d Two extreme positions of bailleadjustment Vare shown in Fig. 2 indicating a possible Arangeofadjustment wl'iich'takes care of various operating conditions in thefilter. In its elevated position the bailleA makes available additionalfiltering area' of the drum, such as would otherwisey be idle. Therespective filtering compartmentsvr then have staggered pulp levels,with one pulp level elevated above the other.

' The `numeral 71 indicates thev feedinlet'into the pre-coatingcompartment for the pre-coating material which may be in the form of apulp 72,

It is i tion step.l It is fedthrough the inlet 71 at a suit- To this endthe inlet for the line` feed in the main filtering lcompartment beingindicated at 73. j

According to a preferred mode oflter peration of this invention, thereis applied diilerential suction to-the pre-coating zone and to the mainfiltering zone respectively, which means that the amount of suctioninthese zones can be adjusted according to vthe filtering characteristicsof the particular material in each compartment. InI the case of baille.adjustment as in the dot and dash position (see Fig. 2), thismeansfurther W that the relative suction may be so adjusted as topreclude an escape of fines from the main filtering compartment backinto the pre-'coating compartment where the lines might reach thesurface of the ltering medium proper.

This feature of differential suction is taken care of by the bridges orpartitions 34 and 35 in the master valve cover, Where the space 74betweenthe bridges defines the range of the precoating 'suction zone,and these bridges may be set in accord with the setting of the baillemember 55.

The preferred filter arrangement as shown in the drawings may beusedwith advantage in the step of gluten filtration in cornstarchmanufacture. The operation thereof is as follows:

The most suitable Isetting of the baffle being determined, the coarsefeed, that is a pulp of corn husks or bran or .the like is fed into theprecoating compartment. This pre-coating pulp is obtained from earliersteps ofthe manufacturing I process and is according to the new practicesuitably disposed of' and filtered in the gluten illtraable rate, whilethe drum rotates in the direction o f the arrow shown, and suction asinduced from the nozzle 4l of the master valve causes the preliminarylayer of coarse material to form upon the filter-elements which aresubmerged in the pre-coating zone. The layer is trimmed to a definitethickness indicated by the numeral 75, as the material passes throughthe clearance between the lower strip 58 of the baille and the ltersurface. As the drum rotates the preliminary layer enters the mainfiltering zone which is dened by the depth of the pulp bath 76 whichconsists of i fines or gluten in suspension.

Since `the, coarse matter or husks are held down by sudtion upon thefilter medium they will stay properly stratied thereon, Whereasotherwise these husks being of relatively low spcic gravity as comparedwith the fine gluten pulp, might go into suspension in that pulp, orelse if mixed therewith as a filter aid would not readily settle.`

The method according to this invention allows proper stratificationdisregarding the relative specific gravity of the ingredients.

The fine or gluten` pulp is shown to be fed through the inlet 73,v and asteady pulp'level 20 135 is. maintained as the' surplus of feedoverflows into the launder 22 over the crimped edge 2l of the opening inthe front end of the drum. The

pre-coating and the main filtering zones are indicated upon thecircumference of the drum (in 14o Fig. 2) by numerals 77 and 78respectively. If

a different degree of suction be applied to each of these zones, it canbe veffected by the proper setting of the bridges 34 and 35 in themaster valve, said bridges then being set in accordance 145 with thesetting of the baille 56 in the drum.

Suctionl through lthe m/ainsuctionv nozzle 42 acts throughthe' primaryvlayer 75 causing a layerv of lines 79 to deposit thereon in the mainfiltering zone. The fines cover the coarse layer in a blanket-likemanner, and suction maintains as the composite cake emerges from thebath, and until it passes on to the cake discharge zone in the topportion of the drum. After the cake reaches the zone above the dischargehopper ,45 the-suction upon the filter elements is released and theusual back-blow applied in order to drop the filter cake into thehopper. The length of the back-blow zone corresponds to the length ofthe port 39 in the master valve cover Where pressure fluid entersthrough the nozzle 40.

Due to the interposed layer of coarse material next to thesurface of thefilter medium the cake detaches readily therefrom, and without leavingtraces of cake or fine particles upon the medium.

In this manner of operation not only a desirable product is obtainedcontinuously from the filtration step, but the filter medium is alsokept continuously in a clean condition.

What I claim is: v

l. In a process of cornstarch manufacture, the method of filtering thevarious grades of byproducts thereof as obtained from wet separationsteps which consists in forming a primary layer of the coarserby-products upon a filter element under suction, and allowing the fineby-products to filter upon said primary layer.

2. In a process of cornstarch manufacture, the method of filteringglutenv which consists in forming a primary layer of corn husks upon atraveling filter element under suction, and allowing the gluten tofilter continuously upon said primary layer.

3. In a continuous rotary filter having a drum, filter elements vthereonadapted to be submerged in a bath' of filtrant, means for producing suc`tion upon said filter elements whereby filter cake is formed thereonduring submergence thereof, a baffle element cooperatively related withthe filter elements in a manner to establish differential filteringzones upon the filter medium, a support for said baflie element, andmeans for adjusting said baffle element relative to said filter elementsand longitudinally of said support.

4. In a continuous rotary filter, having a drum, filter elements uponthe inside of said drum, adapted to be submerged in abath of filtrant inthe drum, means for producing suction upon said filter elements wherebyfilter cake is formed thereon during submergence thereof, a stationarylongitudinal baffle element inside the drum and being cooperativelyrelated with the filter medium in'a manner to produce differentialfiltering zones upon the filter medium, means for supporting the baillemeans within the drum, and means for radial and angular adjustmentl ofvsaid b'afile element relative to the filter medium.

5. In a continuous rotary filter having internal lter panels, adapted tobe submerged in a bath of filtrant in the drum, a master valve forcontrolling the suctionupon said panels, whereby cake is formed thereon,means comprising a baffle element arranged to produce differentialfiltering zones upon the filter panels, and means embodied in the mastervalve for providing differential suction for each zone.

6. In a continuous rotary filter having internal filter panels adaptedto be submerged in a .bath of filtrant in the drum, and a master valvefor controlling the suction upon said panels whereby cake is formedthereon, means comprising an adjustable baffle element arranged toproduce differential filtering zones upon the filter panels,

and adjustable means embodied in the master valve for providingdifferential suction for each filtering zone by timing said adjustablemeans with said adjustable baille element.

EUGENE STARITZKY.

